Devices for measuring or determining the density of a fluid are known per se. The operating principle of such known devices is e.g. based on applying a low-frequency mechanical resonator submersed in a fluid of which the density is to be determined. In this respect, reference can e.g. be made to Patent of the Russian Federation No. 2 291 403, U.S. Pat. No. 4,922,745, U.S. Pat. No. 6,389,891, U.S. Pat. No. 6,845,663. Due to the influence of the added mass of a medium (e.g. a fluid), the resonance frequency of the mechanical resonator changes. Known devices e.g. comprise a measurement circuit for determining an occurring resonance frequency shift which may then be used to calculate a required density value. Known mechanical resonators e.g. include a tuning fork which, due to its symmetric design, prevent the transfer of oscillations to the body of the sensor and, therefore, excludes the influence of the surrounding metal parts on the frequency characteristics of the resonator. To determine the resonance frequency, various electronic circuits can be used, e.g. scanners of the amplitude-frequency response of a resonator or positive-feedback systems self-triggering at a resonance frequency.
Despite satisfactory performance, the known device may have one or more of the following disadvantages.
Firstly, if used to measure the density of a fluid consisting of immiscible components (heterogeneous mixture), like a water-oil emulsion, the properties of a medium surrounding the tuning fork may cause a variation of the resonance characteristic and thus an uncertainty in the resonance frequency measurement, thereby adversely affecting the measurement accuracy.
Secondly, the known device has been found to be unsuited to measure the density of a fluid containing occluded gas, since the presence of such occluded gas may cause considerable and abrupt changes in the resonance frequency thus influencing its mean value and compromising the determination of the fluid density.
In view of the above, it is an object of the present invention to provide a device for determining a density of a fluid with an increased accuracy, in particular for fluids comprising immiscible components (thus forming an heterogeneous mixture), like a water-oil emulsion; or a fluid with occluded gas.